THE  DISSOCIATION  EQUILIBRIUM 
OF  KAOLIN 


BY 

CHARLES  IMSE  ROSE 


THESIS 

FOR  THE 

DEGREE  OF  BAGHELOR  OF  SGIENGE 

IN 

CHEMICAL  ENGINEERING 


COLLEGE  OF  LIBERAL  ARTS  AND  SCIENCES 

UNIVERSITY  OF  ILLINOIS 


1922 


1922 

Pt72 


UNIVERSITY  OF  ILLINOIS 

.May..  20, 1982... 

THIS  IS  TO  CERTIFY  THAT  THE  THESIS  PREPARED  UNDER  MY  SUPERVISION  BY 

.....Cha.ri.e8...Jas.g...^p.g.§, 

entitled .TJae...Dis,s.o.c.ia.ti.oii.,E.quiliU.riun:....Qf  Ka.olm 


IS  APPROVED  BY  ME  AS  FULFILLING  THIS  PART  OF  THE  REQUIREMENTS  FOR  THE 
degree  of B.a.Gii.elo.r....of>...,S.c.i.eii.c.e. 


HEAD  OF  DEPARTMENT  OF. .0.6 r^l.G...Eng.ine.e.Mg 


Digitized  by  the  Internet  Archive 
in  2015 


https://archive.org/details/dissociationequiOOrose 


ACKNOWLEDGMENTS 

/f  ik  kHr  -fc  kik 

The  writer  wishes  to  express  his  appreciation  of 
the  suggestions  and  advice  that  Profe,ssor  E.W. Washburn  has  so 
kindly  given. 

He  also  wishes  to  express  his  thanks  for  the  help 
rendered  by  Dr .E.N. Bunting. 

N 

X*  & -X-  *X*  X*  Xr  X"  X*  X*  X*  X-  X~ 


/ 


TABLE  OF  CONTENTS 

Page 

I.  INTRODUCTION.. 1 

II.  LITERATURE 2 

III . THEORY . . 3 

IV.  APPARATUS  AND  OPERATION 6 

V.  RESULTS  AND  CALCULATIONS 16 

(1)  Data  1'roiri  Static  Method. 19 

(2)  Results  of  Dynamic  Method. 20 

(3)  Heat  of  Dissociation 21 

VI.  CONCLUSIONS 22 


1 


THE  DISSOCIATION  EQUILIBRIUM  OF  KAOLIN 


I.  INTRODUCTION 


A considerable  amount  of  work  has  been  done  in  studying  the 
dehydration  phenomena  of  clays,  and  part  of  this  work  has  been 
concerned  particularly  with  the  rate  of  loss  or  percentage  loss  of 
the  combined  water  of  the  clay  at  various  temperatures. 

The  loss  of  weight  of  clay  samples  or  the  loss  of  chemically 
combined  water  after  heating  the  clay  to  definite  temperatures  has 
been  determined  for  a number  of  them,  but  practically  nothing  has 
been  done  to  ascertain  the  tension  of  the  water  vapor  at  those 
temperatures.  With  this  in  mind  the  problem  of  finding  a method 
or  methods  of  determining  the  actual  dissociation  tension  for  any 
temperature  was  undertaken. 

During  the  trials  a washed  North  Carolina  Kaolin  was  used 

which  is  composed  for  the  most  part  of  the  mineral  kaolinite, 

having  the  formula:  A1  0 . 2SiO  . 2H  0 . This  clay  was  not 

2 3 2 2 

analyzed  except  to  determine  the  average  percentage  of  hygroscopic 
and  combined  water. 


. 

* 


2. 


II.  LITERATURE 

U-.H. Brown  and  E. T .Montgomery1  have  studied  this  clay  among 

1 

Technologic  Paper  No-  21.  Bureau  of 
Standards.  April,  1913 


a number  of  others,  and  have  determined  the  percentage  loss  in  weight 
of  the  combined  water  after  heating  to  certain  definite  temperatures. 
The  graph  obtained  from  their  results  has  been  used  as  an  indication 
of  the  dissociation  tension  that  might  be  expected  since  where 
their  curve  shows  a relatively  large  loss  of  weight  at  a certain 
temperature  one  may  be  led  to  believe  that  the  vapor  tension  will 
show  a relatively  large  increase,  or  will  be  relatively  large  as 
compared  with  the  vapor  tensions  at  any  lower  temperature  provided 
the  temperature  which  produces  the  fastest  rate  of  dehydration  has 
not  been  exceeded. 

A thesis  along  similar  lines  by  Mr.T.K.Chow  which  is  held 
by  this  department  was  occasionally  referred  to  in  order  to  compare 
values  obtained.  This  particular  work  has  results  which  are  of 
doubtful  worth  and  no  great  amount  of  weight  was  given  to  informa- 
tion obtained  from  it. 

Suggestions  for  the  apparatus  have  been  found  in  E. W. Washburn'  i 
. . . 2 

article  y and  also  many  have  been  offered  by  him. 

2 

Jr. Amer. Ceram.  Soc.  37,309  (1915) 


3 


III.  THEORY 

Two  methods  of  attaching  the  problem  were  suggested,  one 
a static  method,  and  the  other  a dynamic  one. 

The  static  method  consisted  of  placing  the  kaolin  in  a 
vessel,  evacuating  the  vessel,  heating  it  in  a small  electric  furnace 
and  then  measuring  the  pressure  of  the  water  vapor  by  means  of  a 
mercury  manometer  sealed  to  the  vessel.  ( See  Fig.1) 

The  kaolin  was  dried  before  placing  it  in  the  vessel  so 
that  most  of  the  hygroscopic  water  would  be  removed. 

When  the  apparatus  was  evacuated  the  mercury  would  rise  in 
the  long  arm  of  the  manometer.  Upon  heating  the  kaolin  some  of  the 
combined  water  would  be  liberated,  and  would  develop  a pressure 
dependent  upon  the  temperature  to  which  the  clay  was  heated.  This 

pressure  would  depress  the  mercury  column  a definite  amount.  By 
noting  the  difference  in  height  of  the  mercury  column  in  the  two 
arms  of  the  U tube,  and  subtracting  this  difference  from  the 
barometric  pressure,  the  pressure  of  the  water  vapor  above  the  clay 
was  obtained. 

1’or  low  pressures  a manometer  tube  was  connected  to  another 
similar  vessel,  and  by  simply  noting  the  difference  in  height  of  the 
mercury  columns  in  the  two  arms  of  the  manometer,  the  pressure  of  the 
vapor  could  be  ascertained. 

It  was  assumed  that  the  water  would  possess  a definite 
vapor  tension  above  the  clay  at  a definite  temperature,  and  that 
repeated  trials  would  give  checji  results. 

making  a sufficient  number  of  trials  at  various  definite 
temperatures,  it  was  hoped  to  obtain  values  to  plot  a curve  showing 


- 


« 

* 


* 

■ 


♦ 


* 


4. 


the  dissociation  tension  of  the  clay  at  various  temperatures. 


The  idea  of  the  dynamic  procedure  was  to  pa3s  a measured 
volume  of  air  over  some  kaolin  which  was  to  be  heated  in  a suitable 
apparatus,  collect  the  moisture  taken  up,  and  then  knowing  the 
weight  of  water  vapor  in  a definite  volume  of  air,  the  pressure  of 
this  water  vapor  could  be  found  by  the  use  of  the  gas  equation. 

( See  Fig. 2. ) 

It  was  assumed  here  also  that  at  any  definite  temperature 
the  kaolin  would  have  a definite  dissociation  tension. 

The  air  in  passing  over  the  clay  was  supposed  to  take  up 
moisture  till  the  partial  pressure  of  the  water  vapor  in  the  air 
was  in  equiliorium  with  the  clay.  Necessarily  the  partial  pressure 
of  the  vapor  in  the  entering  air  would  have  to  be  less  than  the 
pressure  of  the  water  vapor  above  the  clay  if  the  air  were  to  take 
up  any  moisture  in  reaching  equilibrium. 

The  necessity  of  passing  the  air  over  the  clay  at  such  a 
rate  that  the  equilibrium  conditions  would  not  be  disturbed  to  a 
noticeable  extent  was  realized.  The  rate  of  passage  of  this  air 
would  have  to  be  determined  by  experimentation. 

In  order  to  aid  matters  it  was  desired  to  pass  the  air 
through  the  apparatus  in  such  a manner  that  the  air  would  pass  around 
small  pieces  or  particles  of  the  kaolin,  and  not  simply  pass  over 
a layer  of  clay  spread  over  the  bottom  of  the  apparatus. 

Since  any  hygroscopic  water  would  interfere  seriously 
with  the  determination,  this  was  first  removed  before  any  data  were 
recorded. 


- . 


I 


5. 


It  will  be  noted  in  connection  with  this  procedure  that 
the  water  taken  up  by  the  drying  tube®  need  not  come  from  the  cls.y 
entirely,  and,  in  fact,  the  greater  part  of  the  water  was  contained 
in  the  air  in  the  first  place,  since  this  would  allow  equilibrium 
conditions  to  be  reached  in  the  furnace  in  less  time. 


. 

I ■ 


IV.  APPARATUS  AND  OPERATION. 


6 . 


The  vessel  used,  in  the  static  method  was  of  hard  glass, 
and  the  main  portion  which  held  the  clay  was  in  the  shape  of  a flask 
with  a moderately  long  neck.  To  this  neck  was  attached  the  side- 
arms  for  the  vacuum  pump,  and  for  the  manometer  to  measure  the 
pressure  developed. 

The  clay  was  introduced  into  the  flask  through  a hole  in 
the  top  of  the  neck.  After  placing  it  in  the  flask,  the  top  was 
then  sealed  off. 

The  side-arm  for  the  vacuum  pump  was  provided  with  two 
ground  glass  stop-cocxs,  these  stop-cocks  being  about  four  inches 
apart.  The  tops  and  bottoms  of  them  were  sealed  with  wax  when  clos 
after  evacuating  the  bulb. 

The  other  arm  was  in  the  shape  of  a rough  U with  the  half 
of  the  U connected  to  the  flask,  the  longer.  This  half  was  more 
than  long  enough  to  permit  mercury  to  rise  in  it  equal  to  the 
barometric  height.  ( See  Fig.l) . 

This  apparatus  was  placed  in  a small  electric  resistance 
furnace,  the  furnace  being  of  such  size  that  the  side-aims  projected 
over  the  upper  edge  of  it.  The  top  of  the  neck,  and  the  open 

parts  at  the  top  of  the  furnace  were  covered  with  suitable  material. 
The  furnace  was  heated  by  a current  which  could  be  varied  to  suit 
one’s  needs  by  the 'manipulati on  of  a rheostat.  Different 

temperatures  could  thus  be  obtained. 

To  prevent  any  condensation  of  water  vapor  in  the  apparatu 
when  tne  pressure  of  the  vapor  in  it  was  greater  than  the  saturation 
pressure  of  water  vapor  at  room  temperature,  a fine  wire  was 


* 


. -.1  ..  : 


, 


. . 

- §4#  I 


' 


. 


' ■: 


7 . 

wrapped  about  tire  exposed  arms.  This  wire  extended  over  that 
portion  of  the  large  U shaped  arm  not  occupied  by  mercury  when 
pressure  would  be  developed,  and  also  extended  up  to  the  first  stop- 
cock on  the  other  arm.  The  double  stop-cock  was  necessary 

because  this  warming  had  a tendency  to  soften  the  stop-cock  grease, 
and  permit  a slow  leakage  of  air  into  the  apparatus  when  one  was 
used  alone.  A small  current  passed  through  this  wire  was  suffici- 
ent to  warm  all  parts  as  much  as  necessary. 

Temperatures  were  measured  by  a thermocouple,  and  also  by 
an  ordinary  mercury  thermometer,  since  they  rarely  exceeded  400 
degrees  Centigrade  . 

The  diagram  shows  a sectional  view  of  the  apparatus. 

The  dynamic  apparatus  consisted  of  a fused  silica  tube 
about  one  inch  in  diameter,  and  about  four  feet  long.  This  tube 
was  heated  by  passing  a current  through  a nichrome  ribbon  wrapped 
about  it.  The  coils  of  the  ribbon  wera  insulated  from  each  other 
by  alundum  cement,  and  the  entire  heated  portion  of  the  tube  was 
surrounded  with  magnesia  pipe  covering. 

A wet  test  meter  was  used  to  measure  air  volumes.  The 
temperature  of  the  air  coming  from  the  meter  was  read  by  means  of  a 
thermometer  incorporated  in  it. 


■ 


' 


, 


8 . 


When  it  7/as  desired  to  reduce  the  moisture  content  of  this 
air  to  such  a degree  that  the  vapor  pressure  of  this  moisture  would 
be  less  than  that  supposed  to  exist  above  the  clay,  the  air  was 
passed  through  a calcium  chloride  tube. 

Since  only  three  feet  of  the  tube  was  used  as  a furnace, 
it  was  necessary  to  warm  the  exposed  ends  to  prevent  any  condensa- 
tion of  water  vapor  in  them.  The  reason  for  this  was  similar  to 
that  making  it  necessary  to  warm  the  exposed  parts  of  the  static 
apparatus.  A fine  wire  was  wrapped  about  the  exposed  ends,  and  a 
small  current  passed  through  it.  This  current  was  independent 

of  the  heating  current,  and  supplied  all  the  heat  desired, 
it  was  found  from  experience  that  a certain  amount  of  heat  came  from 
the  furnace  and  xept  these  ends  above  room  temperature. 

Issuing  frcm  the  furnace,  the  moisture  laden  air  was 
passed  through  a series  of  six-inch  U tubes  filled  with  calcium 
chloride  and  provided  with  ground  glass  stop-cocks.  Three  tubes 

were  used,  and  they  were  found  to  be  sufficient  to  remove  all 
weighable  amounts  of  water  frcm  the  air.  It  was  also  found  that 
calcium  chloride  was  the  best  agent  since  the  small  pieces  could 
be  placed  in  the  tubes,  and  would  cane  close  together,  but  would 
nevertheless  allow  many  air  passages  between  them,  whereas  if 
sulphuric  acid  had  been  used,  a certain  amount  of  hydrostatic 
pressure  would  have  been  necessary  to  pull  the  air  through  the  tubes, 
and  it  was  desired  to  keep  the  system  at  atmospheric  conditions. 

An  attempt  was  made  to  saturate  small  pieces  of  pumice  stone  with 
the  acid  and  then  fill  the  tubes  with  tn.is,  but  the  acid  dripped 
from  the  pieces  and  collected  in  the  bottoms  of  the  tubes,  and  thus 


9 


defeated  the  purpose  of  this  trial. 

After  passing  through  a stop-cock  in  the  line  used  to  regulate 
the  flow  of  air,  and  a guard  tube  of  calcium  chloride  to  prevent 
any  diffusion  backwards  into  the  absorption  tubes,  the  air  was 
exhausted  either  through  a water  pump,  or  through  an  aspirator  bottle 
The  stop-cock  mentioned  was  placed  in  the  line  at  this  point  in 
order  that  all  the  parts  of  the  apparatus  before  it  would  be  at 
atmospheric  pressure  except  for  the  small  pressure  of  three-twentieths 
of  an  inch  of  water  required  to  operate  the  meter.  By  turning  the 
stop-cock  the  rate  of  flow  could  be  adjusted,  and  by  watching  the 
hand  on  the  dial  of  the  meter  the  rate  of  flow  could  be  measured. 

The  pump  was  a small  ordinary  water  pump,  and  operated  under 
a constant  head.  The  details  of  this  mechanism  are  shown  in  the 
diagram.  It  will  be  noted  that  air  was  pulled  through  the 
apparatus  and  not  blown  through.  The  water  pump  was  used  when  a 
gas  meter  was  available,  as  there  was  no  other  way  of  measuring  air 
volumes  when  it  was  used. 

When  a meter  was  not  available,  another  method  of  finding 
the  air  volumes  was  employed.  This  method  consisted  of  using  an 
asnirator  bottle  to  pull  the  air  through  the  apparatus.  uy  catch- 
ing the  water  coming  from  the  bottle,  weighing  it,  and  finding  its 
volume,  the  volume  of  the  air  pulled  through  could  be  found.  This 
volume  obtained  represented  a volume  of  saturated  air  at  the 
temperature  of  the  water.  nnowing  the  temperature  of  the  water, 
and  its  vapor  pressure  at  that  temperature,  the  actual  volume  of 
air  could  be  found  for  dry  or  otner  c ondit ions . The  barometric 
pressure  was  also  needed. 


c 

- 

■ 

' 

* 

- 

' 

. 

- 

< 

10. 


It  has  been  noted  that  a guard  tube  was  used  to  stop  any 
diffusion  backward  into  the  absorption  tubes.  These  guard  tubes 
were  placed  immediately  in  front  of  the  pump  or  aspirator  bottle 
as  the  case  might  be. 

The  furnace  was  heated  by  a current  which  could  be  varied 
as  desired.  ±>y  using  several  different  currents  in  a preliminary 
test,  the  temperatures  corresponding  to  them  were  found.  From 
these  values  a,  graph  was  plotted  and  enabled  one  to  find  a current 
that  would  give  a desired  temperature.  Direct  current  was  used 
to  avoid  variations. 

The  temperature  of  the  furnace  was  measured  by  means  of 
a thermocouple.  To  test  the  heating  of  the  furnace  the  hot 
junction  of  the  couple  was  moved  along  the  heated  portion  of  the 
tube,  and  the  results  noted.  It  was  found  that  the  furnace  was 
heated  uniformly. 

The  apparatus  was  tested  for  leaks  by  evacuating  it,  and 
then  sealing  it  while  heated.  No  leaks  were  observed.  All 
joints  were  sealed  or  wired  or  both,  and  rubber  stoppers  and  tubing 
were  used  to  make  connections. 

In  later  determi  nations  it  was  found  necessary  to  intro- 
duce a capillary  in  the  line  between  the  exit  of  the  furnace  and 
the  first  absorption  tube.  This  capillary  was  used  to  prevent 
diffusion  of  water  vapor  from  the  heated  clay  into  the  tubes  with- 
out having  air  carry  it. 

Before  loading  the  furnace  the  clay  was  made  into  small 
pellets  composed  of  two-thirds  ordinary  clay,  and  one-third  clay 
which  had  been  dehydrated  by  heating  for  one  hundred  hours  in  a 


-r 


1 

■ 


, 


11. 


high  vacuum.  These  pellets  were  broken  into  small  pieces  prelim- 
inary to  pushing  them  into  the  furnace,  but  were  not  broken  into 
small  particles.  They  were  then  pushed  into  the  furnace,  and 
filled  the  heated  portion  to  within  too  or  three  inches  of  each  end 
of  it.  This  insured  the  clay  being  heated  uniformly.  The  pur- 
pose of  this  breaking  of  the  pellets  was  to  provide  as  much  surface 
as  possible,  and  to  allow  the  air  to  circulate  around  the  small 
pieces  instead  of  simply  over  them.  Since  the  pieces  were 
irregular  there  were  many  small  openings  that  the  air  could  pass 
through.  Had  the  furnace  been  filled  with  the  fine  particles 

it  would  have  been  completely  stopped  up,  or  if  a less  amount  had 
been  used  then  a layer  would  have  formed  at  the  bottom  of  the  tube 
and  the  air  would  have  passed  over  the  clay. 

Before  collecting  any  moisture  or  measuring  any  air 
passing  through  the  furnace  the  apparatus  was  allowed  to  come  to  a 
constant  temperature.  After  this  haa  been  attained  the  absorption 
tuoes  were  placed  in  the  line.  These  tubes  were  previously 
connected  togetner  by  small  pieces  of  rubber  tubing  which  were 
wired  fast  to  the  side-arms.  Then  all  joints  were  sealed  and  in- 
spected, the  stop-cocks  on  the  calcium  chloride  tuoes  were  opened* 
The  regulating  stop-cock  was  opened  a slight  amount,  and  air  was 
slowly  drawn  through  the  apparatus.  The  opening  ol  the  main 

s t op  - c o c had  to  be  adjusted  for  each  run. 

The  data  necessary  were  the  air  volume  and  its  temperature 

when  issuing  from  the  meter,  the  weight  of  the  water  taken  up  by 
the  calcium  chloride  tubes,  the  barometric  pressure,  r.nd  the 


- 


El  Eli-  -t  I- J| 


■ 

. 


. 


- 


; 


12. 


temperature  of  the  furnace. 


\ 


Dynamic  Apparatus 


16 


V- RESULTS  MU  CALCULATIONS 

The  static  method  showed  that  the  kaolin  adsorbs  a large 
amount  of  air  which  is  given  off  slowly  when  the  clay  is  heated,  and 
which  seriously  interferes  with  the  measurement  of  the  vapor  pressure. 
Its  presence  was  detected  in  the  apparatus  by  observing  that  when 
the  manometer  tube  was  at  room  temperature  there  was  no  condensation 
of  water  vapor  on  the  inside  walls,  of  the  tube  though  the  pressure 
measured  was  far  in  excess  of  that  allowed  for  saturation  pressure 
of  water  vapor  in  air  for  the  same  temperature.  There  were  no 
leaks  in  the  apparatus  when  these  observations  were  made.  The 
air  is  held  tenaciously  by  the  clay,  and  is  only  removed  after  a 
long  period  of  heating  in  the  exhausted  vessel.  When  all  of  the 
air  was  removed  most  of  the  water  of  the  clay  had  been  removed,  and 
no  reliable  results  could  be  obtained. 

Due  to  factors  mentioned  above,  and  also  the  development  of 
leaks  in  the  apparatus  occasionally  but  at  an  important  time, no 
results  of  any  value  were  obtained  with  the  static  apparatus  with 
the  open  manometer  tube. 

I’or  low  pressures  the  closed  manometer  tube  apparatus  was 
used,  and  some  check  results  were  obtained  over  a moderate  range  of 
temperatures.  These  results  were  obtained  after  cooling  and 
heating  several  times,  and  after  all  air  had  been  removed  from  the 
clay.  The  mass  of  clay  used  with  this  particular  piece  of 

apparatus  was  considerably  less  than  in  the  case  of  the  other  piece. 
(See  Graph  II).  I'rom  the  data  obtained  from  this  test  another 

curve  was  plotted  as  shown  in  Graph  III. 


- 


- 


. 


. 


•• 


340 


320 


t i 

300  g 

•H 
-P 
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0) 
o 


280 


260 


CO 
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0) 
h 
W 
0) 

240  « 
«» 

p 

-Hlfn 

0) 

ft. 

200  | 

e-i 


180 


220 


160 


140 


Graph  II 

Pressure-Temperature  Curve 


8 


Vapor  Pressure  in  mm.  of  Mercury, 
10  12  14  16 


18 


Curve  from  Van’t  Hoff  equation. 


0017  . C018  .0019  Wlm  .0071  .007 


19. 


Data  from  Static  Method, 

Temperature  Degrees  Pressure  of  vapor 

Centigrade  in  mm.  liercury 


145 

9.0 

190 

10.5 

235 

13.5 

260 

14.0 

275 

16,0 

300 

X7 .0 

The  dynamic  method  was  not  influenced  by  adsorbed  air. 

This  method  snowed  tnat  tne  clay  was  very  slow  in  approaching 
equilibrium  as  did  the  static  method. 

When  air  was  passed  through  the  apparatus  slowly,  about 
two-tenths  of  a cubic  foot  per  twenty-four  hours,  water  vapor  from 
the  furnace  diffused  over  into  the  absorption  tubes,  and  thus 
made  the  results  high.  When  air  was  passed  through  too  quickly 
the  equilibrium  was  disturbed,  and  a low  value  for  the  pressure 
was  always  certain  to  be  the  result.  This  diffusion  was  prevented 
in  the  last  part  of  the  work  by  introducing  a short  piece  of 
capillary  tubing  in  the  line  between  the  end  of  the  furnace  and  the 
absorption  tubes. 

Although  adsorbed  air  did  not  influence  the  results  here, 
check  results  could  not  be  obtained  although  the  manipulations 
carried  out  in  each  test  at  the  same  temperature  were  exactly 
alike*  Care  was  taken  to  see  that  any  hygroscopic  water  was  re- 


! 


- 


; . - 

' H ■ 


20. 


moved  before  any  run  was  made,  and  that  the  clay  in  the  furnace 
was  net  dehydrated.  When  any  clay  became  dehydrated  it  was  removed 
and  replaced  by  other  material  . 

Results  of  Dynamic  Method 

Temperature  Degrees  Pressure  of  Vapor 

Centigrade  mm.  of  Llercurv 


317 

9.39 

320 

7.96 

433 

93.26 

200 

3.69 

175 

1.47 

293 

7.06 

297 

7.04 

320 

7.49 

322 

13.18 

322 

2.80 

352 

12.93 

322 

15.61 

322 

5.7 

347 

3.14 

The  volume  and  temperature  of  the  air  were  known,  and  by 
subtracting  the  saturation  pressure  of  water  vapor  in  air  from  the 
barometric  reading,  the  pressure  of  the  air  was  found.  Using 
these  three  quantities  in  the  gas  equation,  gave  the  moles  of  air. 
The  moles  of  water  could  be  found  from  the  gain  in  weight  of  the 


21. 


absorption  tubes.  We  had  then  that  : 

ptr  n : P : : N : Ny  air  from  which  the  pressure  of  the 

n2°  HO  H2° 

2 

water  vapor  could  be  found. 

Heat  of  Dissociation. - The  heat  of  dissociation  for  one 
mole  of  water  was  found  by  the  use  of  the  formula: 


log 


P 


H 

R 


f-1 - ...  A—  ) 

V * h ) 


where  the  pressures  and  temperatures  used  were  those  obtained  from 
the  static  method  det erminations . 


p =9.0 
1 

p = 17 
2 


T = 145  + 273  = 418° 
1 

T = 300  + 273  = 573° 
2 


log  9.0 


= -0.5353 


e 1,7 
1 =0.00239 


1 =0.00174 

T 

2 


(1  - 1 ) =-0.00065 

T T 

2 1 


H 

.0*0353  = p 


1.985 


( -0.00065) 


H = 1940  calories  per  mole  H 0 
P 2 

H = 1940  = 107.8  calories  per  gin.  HO 

p 18  2 


22. 


VI.  CONCLUSIONS 

Since  the  values  obtained  by  the  static  method  could 
be  reproduced,  they  may  be  taken  as  approaching  the  correct  values. 

Results  from  the  dynamic  method  are  low  in  comparison 
v/ith  those  obtained  by  the  static  procedure, as  might  be  expected. 
The  highest  value  given  by  the  dynamic  method  would  be  the  nearest 
to  the  correct  value,  and  even  then  might  be  considerable  short 
of  it . 


. 


■ 


